DETROIT (Reuters) - Eight employees at Volkswagen AG's Tennessee plant have said they were misled into endorsing the United Auto Workers, handing some ammunition to opponents of the union's efforts to organize for the first time at a foreign-owned U.S. factory.

The UAW has countered that the complaints, which were filed with the National Labor Relations Board, are a "frivolous and baseless" attempt to delay negotiations between the union and Volkswagen.

The complaints challenge the validity of cards signed by the workers. The UAW says a majority of the 1,567 production and maintenance workers at VW's Chattanooga plant have signed cards supporting the union.

A majority would allow the automaker to install the union without a formal vote if it so desired and the UAW has said it wants to avoid a vote as it might divide the workforce.

The UAW is keen to install a "German-styled" works council that will represent both blue- and white-collar employees at the plant. But only the blue-collar workers would be represented by the UAW, which would negotiate their wages and benefits.

But the National Right to Work Foundation, an anti-union group that filed the complaints on behalf of the workers, said the workers claimed UAW organizers told them that signing the cards was not an endorsement of the UAW but instead called for a secret ballot on union representation.

The complaints ask the National Labor Relations Board to order UAW union officials "to cease and desist from demanding recognition based upon the tainted cards."

In response, Gary Casteel, regional director in the Southeast for the UAW, said the cards signed by the workers clearly state the workers are supporting the UAW's effort to represent them. The cards, seen by Reuters, include the line: "We choose to be represented by the UAW."

Casteel added that "substantially less" than eight workers have asked to have their signature cards revoked.

Complaints like these usually take about two months for the labor relations board to investigate and offer an opinion on them, said National Right to Work attorney John Raudabaugh.

The anti-union group is pushing for a formal vote, saying that only a vote would reveal the true intentions of the workers and that not holding a vote would be undemocratic.

Casteel said the complaints will not affect the talks between Volkswagen and the union.

Another key issue over the cards has been whether workers can easily revoke them.

The National Right to Work Foundation said the UAW makes it easy for workers to sign the authorization cards at the workplace but the workers must go to the union office to reclaim their cards.

The UAW said it has made clear that the cards can be revoked. It supplied Reuters with letters Casteel said were sent on February 19 and June 13 to all workers who had signed union authorization cards that said: "If you are uncomfortable with our commitment...you are free to revoke any card you have signed by notifying us of your desire to do so."